This invention relates to differential assemblies for use in automobiles, and more particularly to differential assemblies of the type having a lock ring installed on each differential shaft for equalizing the distribution of the torque applied to each portion of the drive axle driving each wheel during initial acceleration.
In the field of automotive engineering, the power generated by the engine is transmitted to the wheels along a drive shaft via the transmission and the differential assembly. Drive trains may be designed for a plurality of applications including a rear wheel driven vehicle having a rear mounted engine and transmission, a front wheel driven vehicle having a forward mounted engine and transmission or a front mounted transverse engine having a forward mounted transmission and differential assembly referred to as a transaxle.
In particular, certain designs include the engine mounted adjacent to the differential assembly with the transmission situated therebetween. Various designs are possible depending upon the articulated linkage. The transmission includes an output pinion shaft having a pinion gear mounted on the end thereof. The pinion gear interfaces with an outer ring gear mounted on the outer housing of the differential assembly. The purpose of the differential assembly is to transfer the power from the pinion gear to the wheels via the ring gear and a pair of differential shafts.
The ring gear is generally bolted to the differential housing and to a differential cover. Thus, when the ring gear is rotated by the pinion gear the entire differential assembly rotates in the same direction while a carrier bearing permits the differential assembly to spin freely within a transmission housing. A pair of differential shafts are mounted within the differential housing for transmitting the torque applied to the ring gear to the vehicle wheels. The first differential shaft has a gear attached to one end and a set of splines machined into the opposite end. The splined end passes through the differential housing and the far end of the ring gear. The second differential shaft also includes a gear and a splined end which extends through the differential cover bolted to the differential housing.
Each splined end further includes a thrust washer mounted thereover between each differential shaft and respectively the differential housing or the differential cover. In essence, the thrust washer functions as a bearing surface to maintain alignment of the differential shafts for preventing excessive wear in the differential housing and the differential cover.
Within the differential housing, the two differential gears are separated and aligned by a spacer sleeve having a vertical penetration therethrough. Passing through the vertical penetration is a spider shaft having one of a pair of spider gears mounted on each end thereof. The spacing is such that the differential gears and the spider gears mesh. Thus, rotation of either differential shaft will cause movement in the individual meshed gears. The spider gears provide a partial independency between the vehicle wheels by permitting the differential gears to operate independent of one another.
In general, the differential housing and the spider shaft rotate with the ring gear within the transmission housing. The rotation of the spider shaft drives the spider gears and the differential gears on the differential shafts which pass through the differential assemby for driving the wheel.
During initial acceleration, a characteristic of the transmission is to apply the engine torque to only a single drive wheel. The power is transmitted to either a right mounted or a left mounted ring gear by the pinion gear, depending upon the design of the drive train. Consequently, either the right wheel or the left wheel initially receives the torque from the engine because the ring gear is located on the thrust side of the transaxle. The inertial resistance of one wheel is higher than that of the opposite wheel and the positioning of the ring gear permits the wheel with the lower inertial resistance to be driven.
Several problems were created due to this torque distribution to the wheels. A first problem was that upon acceleration of the vehicle, only one wheel was capable of providing traction to the vehicle. Under normal conditions, traction from only a single drive wheel is sufficient; however, if the vehicle was entrapped, as in mud, a single drive wheel was often inadequate to provide forward motion. Under these conditions, the driven wheel during acceleration would spin while the non-driven wheel was permitted to freewheel. Further, the differential assembly on the side receiving the initial torque during acceleration would experience rapid wear requiring excessive maintenance and overhaul.
A method was developed to more evenly distribute the initial torque to each wheel during acceleration. The method included inserting a tapered ring between the differential housing and the differential shafts. Generally, the tapered ring was circular having a plurality of radial grooves machined into the outer circumference for the purpose of passing lubrication therethrough. At the outer circumference along the longitudinal axis of the ring, there was a pair of unrelieved rectangular corners. The tapered ring was designed to lock the differential shafts respectively to the differential housing and the differential cover. In actual operation, one of the tapered ring was fitted over each of the splined ends of the differential shafts. Each of the tapered rings were seated within an interior recess at the point where each differential shaft extends from the differential assembly.
Each of the tapered rings included a forty-five degree angled cut which, by design, provided a spring-like effect. The spring-like effect would cause the differential shafts to be locked respectively to the differential housing and differential cover so that if the drive wheel became entrapped, the tapered ring permitted the initial torque to be applied to both drive wheels during acceleration permitting the vehicle to escape.
With the advent of the tapered ring, additional problems were created. The forty-five degree angled cut on the tapered ring included a pair of faces which, if misaligned during installation, would interfere with one another causing the tapered ring to fail to lock the housing and cover to the differential shafts. Further, the tapered ring would operate properly only if the differential shaft was rotated in a specified direction.
Still another problem was that the tapered ring was subject to fracture during the slightest impact. Thus, if either one of the drive wheels bumped a curb, the tapered ring would fracture notwithstanding the fact that the other components in the differential assembly were not damaged. It has been observed that the tapered ring tends to fracture at the unrelieved rectangular corners. The fracture would result in a release of the spring-like lock between the differential shafts and respectively the differential housing and cover resulting in the torque again being applied to the single driven wheel during acceleration. Further, the fractured tapered ring would cause a loud grinding noise within the differential assembly which was a nuisance.
Hence, those concerned with the development and use of differential assemblies in motorized vehicles have long recognized the need for improved distribution of the initial accelerating torque to the drive wheels for eliminating the fracturing of the tapered ring which locks the differential shafts respectively to the differential housing and cover and for improving the design of the tapered ring at the situs of the fracture. Further, there is a need for an improved tapered ring for reducing the excessive wear of components on the thrust side of the differential assembly which may ultimately result in the fracture of the differential gear shaft from the torque initially applied to the driven wheel during acceleration. The present invention fulfills all of these needs.